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Specific surface area measurements of The Clay Minerals Society source clays were made by the Brunauer, Emmett and Teller (BET) method of adsorption of nitrogen gas. Two replicate measurements of specific surface area were performed for each source clay. All pair values were within 3%, which is very good agreement for this type of measurement.

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A new equation, a modified Langmuir-like equation (M-LLE), for describing adsorption from solution by activated carbons is proposed for the first time in this work. The M-LLE assumes that there are two types of interactions: (a) specific interactions which are typical, enthalpy-driven interactions and (b) nonspecific interactions driven by the loss of water structuring, upon adsorption (hydrophobic bonding), around the nonpolar parts of the drug. The proposed model was evaluated by studying the adsorption of three drugs: procaine, fluoxetine, and phenobarbital by four different activated carbons under different experimental conditions. As the hydrophobicity of the drug increased, the capacity constant representing the interactions driven by hydrophobic bonding (K(HB), M-LLE equation) increased. Experimental conditions that decrease hydrophobic bonding, such as increased temperature and higher cosolvent concentration, resulted in a decrease in K(HB). Salts that tend to increase water structuring and hydrophobic bonding caused an increase in K(HB). All of these studies support the M-LLE, because they support the notion of hydrophobic-bonding-driven interactions.

The Clay Minerals Society published a complete characterization scheme for its ‘Source Clays’ but not for its ‘Special Clays’. To address this issue, the specific surface areas (SSAs) of the 16 special clays from The Clay Minerals Society were determined using the Brunauer, Emmett and Teller (BET) method of adsorption of an inert gas. Two BET measurements were performed for each of the 16 special clays, and the average BET SSA of each of the special clays was determined. The BET SSA of cookeite is reported for the first time. In the present study, special clays from The Clay Minerals Society are classified under three groups based on their BET special surface area values as Group-I special clays, with BET values of 0.1–10 m2/g, Group-II special clays, with BET values of 10–100 m2/g, and Group-III special clays, with BET values >100 m2/g. Comparisons which proved interesting were the those involving the mixed-layer clays and the synthetic clays. The systematic approach employed in this paper will allow for better comparisons to be made between different clays and will provide a comprehensive database for future applications of such material (e.g. as catalyst carriers, as adsorbents in waste treatments, etc.).